A centrifugal compressor of the type above mentioned is used mainly in a gas turbine and is designed and engineered to satisfy two major requirements. One requirement is to reduce the fluid friction loss in the compressor so as to achieve a high compression efficiency. The other requirement is to preclude an occurrence of surging when the compressor is operated at low fluid flow rates. Provision of a fluid diffuser having variable-angle vanes is used for meeting these two requirements.
For the purpose of reducing the fluid friction loss in the compressor to a minimum, it has been proposed to design the compressor in such a manner as to reduce the distance between each of the variable-angle diffuser vanes and a fluid impeller around which the diffuser vanes are circumferentially arranged. Drawbacks are however encountered in a prior-art fluid compressor of this type in that the compressor tends to produce increased amounts of noise and in that shock waves are produced between the impeller and the diffuser vanes and cause deterioration in the output performance of the compressor. If, furthermore, the diffuser vanes are arranged to lie more closely to radial directions of the diffuser so as to reduce the distance between the impeller and the diffuser vanes, the compressor will cause surging at low fluid flow rates. If, on the contrary, the diffuser vanes are arranged to lie closer to the circumferential direction of the diffuser, the occurrence of surging will be precluded but, instead, an increase in the fluid friction loss in the compressor will result.
The present invention contemplates provision of an improved centrifugal fluid compressor eliminating these drawbacks which have thus far been encountered in a prior-art centrifugal fluid compressor having a fluid diffuser with variable-angle diffuser vanes.